1. Field of the Invention
The present invention relates to sensors for use in medical procedures, and more specifically, it relates to a fiber optic biosensor for the diagnosis and treatment of stroke-related conditions. More specifically, it relates to a biosensor which can be used in vivo in endovascular procedures, integrated with a catheter, for the diagnosis of thrombus (blood clot) type and to provide guidance in the use of thrombolytics for clot dissolution (e.g., dose and dose rate). It can be used in conjunction with other therapies, such as laser thrombolysis.
2. Description of Related Art
Stroke is the third leading cause of death in the United States, costing an estimated $15-30 billion per year. Most strokes are caused by vascular occlusion due to cerebral atherosclerosis or to thromboemboli of the extracranial or intracranial blood vessels. When vascular occlusions occur, such as in the carotid artery, blood flow to the brain is impeded, leading to stroke.
Interventional neuroradiologists and neurosurgeons have devised elegant procedures for treating stroke. Through use of microcatheters they are able to insert coils into aneurysms, perform balloon angioplasty on calcified deposits, and administer thrombolytic agents. Thrombolytic therapy is a minimally invasive procedure which involves directing a microcatheter to the site of an occlusion and releasing thrombolytic agents directly into a clot. If the clot is composed of cross-linked fibrin (i.e., soft vs. calcified) the clot will lyse producing fibrinolytic products. With regard to diagnosis, the most important of these fragments is D dimer, which is composed of crosslinked gamma chain remnants.
There is currently available an in vitro test for D dimer. This test, performed in hospital clinical laboratories is often ordered for patients presenting stroke symptoms. The test is based upon agglutination. A plasma sample from the patient's blood is mixed with a solution containing the antibodies supplied with the test kit. If the solution becomes cloudy (agglutinates), the presence of D dimer is indicated. The level of D dimer is determined (very roughly) by performing this test using successive dilutions of the patient's blood plasma. This test only determines the systemic presence of D dimer.
A sensor for D dimer would find widespread use as an important diagnostic tool in marking ischemic events. Used in vivo, it could obtain localized information in the vascular system. As a diagnostic tool, it would be valuable because it could distinguish, locally, whether an occlusion is caused by atherosclerotic plaque or thrombus. A D dimer sensor would be useful in providing guidance for dosage and infusion rates of thrombolytic agents. Most importantly, it should be usable in isolated therapy procedures (e.g., double balloon) to detect when a thrombus was completely lysed and whether restenosis was occurring following therapy.
Fiber optic sensors are well known in the literature. They have been used for environmental and medical applications. Enhancement of sensitivity and selectivity has been obtained using coatings applied to the fiber optic core. When used as biosensors, a biologically-active component is an integral part of the coating. If these biologically-active components are antibodies, then the biosensor is specifically an immunosensor. When immersed in the environment of interest, antigens diffuse into the coating and bind with the antibodies. The binding process forms the basis for detection. Specifically, if the antibodies are "tagged" with a fluorescent molecule, when the antigen binds there will be an effect on the spectroscopic properties of the "tagging" molecule. Fiber optic biosensors using this detection scheme are well known.